Diffusion and Osmosis

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Diffusion and Osmosis
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Outline

• Learn the concepts of
• Diffusion, osmosis, semi-permeable membrane,
  isotonic, hypertonic, hypotonic
• Explore diffusion in a colloid
• Relationship between diffusion size
• Explore diffusion osmosis in a dialysis bag
• Dialysis bag experiment
• Semi-permeable membrane
• Water, glucose, starch
• Plant/animal cells exposure to water
• Hypertonic Env.
• Hypotonic Env.
• Isotonic Env.

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Diffusion

• Solute molecules moving from an area of high
  concentration to an area of low concentration
• Random motion drives diffusion
• Movement is based on kinetic energy (speed),
  charge, and mass of molecules
• Equilibrium is reached when there is an even
  distribution of solute molecules

(water)
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Osmosis

• Diffusion of water through a semi-permeable
  membrane
• Semi-permeable permeable to solvents (WATER),
  but not to large molecules
• High water to low water
• Dissolved molecules (i.e. glucose, starch) are
  called solutes
• REMEMBER
• Water solvent
• Glucose, Starch solutes

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Diffusion Rates of Various Dyes

• How do different MW solutions migrate through a
  colloid?
• Colloid suspension of large, insoluble
  particles in a fluid medium
• Agar plate
• Measure the rate of diffusion of various dye
  (differ in MW)
• Measure diameter at T90 (minutes)

• 3 known(s) (crystal violet, malachite green,
  potassium permanganate)
• 3 unknowns

Part 1 pg. 82
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Diffusion Rates of Various Dyes

• How do different MW solutions migrate through a
  colloid?
• Standard Curve
• Y-axis molecular weight (MW)
• X-axis distance migrated (mm)

?

• Inverse Relationship
• Higher MW, slower diffusion
• Lower MW, faster diffusion

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Dialysis Bag Experiment

• Dialysis Bag
• Semi-permeable membrane
• Water, glucose, starch
• What passes through the dialysis bag?
• Glucose (Benedicts Test)
• Starch (Iodine Solution)
• Time Course Experiment
• Every 10 minutes, measure the amount of glucose
  starch present in the beaker

Part 2 pg. 83
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Dialysis Bag Experiment - Results
Lab Manual, page 84
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Dialysis Bag Experiment - Controls

• Negative control for dialysis bag experiment
  (performed by TA)
• Instead of using dialysis tubing, I will be
  using a plastic bag.
• I will determine the weight, Benedicts result,
  iodine results at time 0 and 80 minutes
• Biochemical test controls (in pairs)
• set up test control of iodine test w/ glucose
  and starch
• set up test control of Benedicts test w/
  glucose and starch

Iodine Benedicts
Glucose ? ?
Starch ? ?
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Effect of Water on Cells

• Hypertonic Environment
• High solute, low water
• Hypotonic Environment
• High water, low solute
• Isotonic Environment
• water solute

Hypotonic
Hypertonic
Isotonic
Part 3 pg. 85
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Osmosis in Living Cells
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Osmosis in Red Blood Cells

• Observe sheep RBCs via a wet mount of the sample
• Aliquot one drop the following solutions with a
  ½ drop of RBC to a slide
• 0.9 saline
• 10 NaCl
• Distilled water
• Record observation in the table on page 85

Crenation
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Osmosis in Plant Cells
Plasmolysis

• Observe Elodea leaves via a wet mount of the
  sample
• Aliquot two drops the following solutions with a
  new Elodea leaf to a slide. Incubate for 10
  minutes _at_ room temp.
• 10 NaCl
• Distilled water
• Record observation in the table on page 85

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Plan of attack . . .

• Set-up Part I Molecular Weight Diffusion in
  Colloid
• Incubate for 90 minutes
• Set up Part II Dialysis Bag
• Time course 80 minutes (time-point every 10
  minutes)
• Part III Osmosis in Living Cells

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Animations

• Dialysis Bag Experiment
• http//ccollege.hccs.cc.tx.us/instru/Biology/AllSt
  udyPages/Diffusion_Osmosis/Baggif.swf
• Elodea Cell
• http//ccollege.hccs.cc.tx.us/instru/Biology/AllSt
  udyPages/Diffusion_Osmosis/Elodeagif.swf
• Osmosis
• http//ull.chemistry.uakron.edu/genobc/animations/
  osmosis.mov

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Transportation of Molecules

• Passive Transport
• Movement of molecules across a semi-permeable
  membrane
• no energy required
• Active Transport
• Movement of molecules across a semi-permeable
  membrane against a concentration gradient with a
  protein
• ENERGY ATP
• Facilitated Diffusion
• Movement of molecules across a semi-permeable
  membrane with a protein
• no energy required

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Effect of Water on RBC
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